For the purpose of providing a background and introduction to the present invention, reference is hereby made to the following earlier patent applications, namely:                International Patent Application No. PCT/AU2015/050161 (hereinafter referred to as “patent application '161”);        International Patent Application No. PCT/AU2015/050384 (hereinafter referred to as “patent application '384”); and        Australian Innovation Patent Application No. 2016101994 (hereinafter referred to as “patent application '994”).        
The entire contents of the earlier patent applications listed above are hereby incorporated herein by reference. However, in the event of (or to the extent of) any inconsistency or discrepancy between the disclosure in the present specification and the disclosure in any of the earlier patent applications listed above, the present specification takes precedence and overrides. Also, the mere incorporation herein of the contents of the earlier patent applications listed above does not mean that any express or implied restrictions or limitations on any inventions disclosed in any of those earlier patent applications, or that any express or implied restrictions or limitations on any other disclosure(s) given therein, necessarily also apply to the present invention or the disclosures herein.
In the context of road vehicle detection and identification through RFID, patent applications '161 and '384 in particular explain, inter alia, that there are a number of significant benefits and advantages that can arise from placing an RFID tag fairly low-down on a vehicle (i.e. quite close to ground/road height), preferably by placing a tag on one or both of the vehicle's license plates (or by embedding a tag in one or both of the vehicle's license plates thereby making the license plates “smart” plates), and also from enabling the said RFID tag(s) to be read by an RFID reader, the antenna of which (at least) is placed on or in the road. Many reasons for this are explained in detail in patent applications '161 and '384.
It is to be noted that the proposal in the previous paragraph, namely placing RFID tags low on vehicles (preferably by having the tags on or embedded in license plates) and enabling the tags to be read by an RFID reader which has (at least) its antenna placed on or in the road, represents a major departure from the design and thinking behind conventional RFID systems used for vehicle detection, identification and/or monitoring. Indeed, in most conventional RFID-based vehicle detection, identification and/or monitoring systems, an RFID tag is installed on the inside of a vehicle's windscreens (i.e. quite high up on the vehicle), and the RFID tags on the vehicles are read by RFID readers mounted (very often) “overhead”, generally on over-road gantries or the like. These conventional systems incorporating windscreen-mounted RFID tags and over-road or gantry based RFID reader placements suffer from numerous disadvantages, as discussed more in patent applications '161 and '384. However, of the many disadvantages, one of the most significant is quite simply the cost associated with over-road gantries, both in terms of the cost of producing the gantries themselves (they are large metal structures), and also in terms of costs associated with erection of the gantries over the roads, and the installation of the RFID reader equipment thereon, etc, as well as any subsequent maintenance or repair of the gantry and/or reader equipment, all of which generally require partial or complete closure of the road (which is in turn extremely disruptive and expensive in itself, quite apart from the actual costs associated with the maintenance or repair).
Patent applications '384 and '994 describe the design and configuration of certain antennas, and RFID readers incorporating said antennas, that may be capable of on-road or in-road installation or deployment and which may also be suitable (when installed/deployed on or in the road) for reading RFID tags on passing vehicles' license plates, including on freeways or other roads with high (or potentially high) vehicle speeds. The antennas and RFID readers described in patent applications '384 and '994, and other associated disclosures therein, therefore provide a possible alternative to conventional RFID systems in freeway and open road scenarios which rely on over-road gantries and the like. Use of the antennas described in patent applications '384 and '994 may therefore allow a number of the major disadvantages associated with over-road gantries or the like, including (in particular) the cost thereof, to be avoided or reduced, whilst still allowing vehicle detection and identification, etc, using RFID.
For the purposes of the present introduction, it is to be noted that, where an antenna is installed/deployed on or in the road and is to be used for reading RFID tags on passing vehicles' license plates, particularly on freeways or other roads with high (or potentially high) vehicle speeds (and it is believed that the antennas described in patent application '384 and/or '994 are suitable/capable of use in these kinds of high-speed applications), there is a required read zone for the antenna which is actually quite specifically defined in terms of its size and shape. In other words, there is a region of quite specific size and shape near the RFID reader antenna inside which the RFID reader is required to be (i.e. it must be) able to communicate with a vehicle's plate-mounted RFID tag if (or whenever) a vehicle's tag is within the said region. The reason this required read zone (region) is quite specifically defined in terms of its size and shape is due to a number of factors, including: the geometry associated with the placement location and orientation of license plates on vehicles, the dimensions (especially the width) of road lanes, the typical maximum speed of travel of vehicles (especially on freeways and other high (or potentially high) speed roads), and the time required for an RFID reader to reliably “read” (i.e. detect and positively identify) a vehicle's (plate-mounted) RFID tag. This is all explained in much greater detail in patent applications '384 and '994.
Also, for the purposes of the present introduction, it should be noted that, for “open road” and freeway applications especially (where vehicle speeds may be high), there is also generally a need to be able to detect and identify a vehicle which could potentially be at any location within a road lane, including perhaps even at a position across or straddling multiple lanes if the road has more than one lane. What this means is that, in these kinds of “open road” and freeway applications, there is (or there may often be) a need to be able to detect and positively identify passing vehicles notwithstanding the fact there is often considerable uncertainty as to the actual location of a vehicle (i.e. where the vehicle will actually be relative to the antenna) as the vehicle passes the antenna. There may also be a need to be able to detect vehicles moving in different directions relative to the antenna, for example, if the antenna is placed at a crossroads or at an intersection where different vehicles may pass over or pass by the antenna while travelling in different directions. As a result of these things, RFID reader antennas which are capable of on- and/or in-road placement and which are suitable for reading RFID tags on passing vehicles' license plates on freeways or in other open road applications should generally have (or at least it is desirable for them to have) a radiation pattern that “points” in most, if not all, radial directions around the antenna. In other words, the antenna's radiated energy must (at least preferably) propagate in all radial directions, preferably approximately or substantially equally in all radial directions. Thus, for freeway and other open road applications especially, the antenna should preferably be (at least substantially) non-directional (or omni-directional). In addition, the amount of energy radiated in an “upward” direction (i.e. the amount of energy directed vertically upwards perpendicular to the surface of the road) should be limited. There are a number of reasons for this, including limiting potentially “blinding” energy reflections from the undersides of vehicles that pass over the top of the antenna.
Designing an antenna which is able to provide a radiation pattern that meets or balances the above-summarised requirements has proven to be extremely challenging, although the antenna designs described in patent applications '384 and '994 are presently considered to be promising, and one or more of them are thought to be commercially viable, including for “open road” and freeway applications.
As mentioned above, in open road and freeway scenarios (and hence at locations where vehicles are to be detected and positively identified in these scenarios), vehicles are generally (or they can be) moving at high speed. As an indication (albeit without limitation), for design purposes, an assumption is often made that on freeways and open roads, vehicles may be travelling up to (or around) 180 km/h, or at least at speeds of this order. In any case, as a result of the potentially high vehicle speeds on freeways and other open roads, it is often the case that a vehicle that is passing an RFID antenna on a freeway or open road, and whose plate-mounted RFID tag must be read by the RFID reader associated with the antenna, will only be in the antenna's “read zone” for a very short period of time (due to the speed at which the vehicle moves past the stationary antenna). As a result of this, in these kinds of high vehicle speed scenarios, there is sometimes a need (or perhaps a desire) to supply a high amount of power to the on- or in-road antenna (to the extent possible or permitted by regulation). This is to try and increase or maximise the size of the antenna's “read zone”, because if the size of the “read zone” near the RFID antenna is increased, then the amount of time that the vehicle is within that “read zone” as it passes the antenna will also likely increase, thus giving more time for the RFID reader to detect and positively identify the vehicle through communication with the RFID tag on (at least one of) the vehicle's license plates. However, simply increasing the power supplied to the RFID reader antenna in order to increase the size of the antenna's “read zone” (for the purpose of providing a greater amount of time to perform RFID communication with vehicles' plate mounted RFID tags) is not always viable, or even permitted. For one thing, there may be limits on the amount of power that can be supplied to the antenna, e.g. due to limits on the power that can be easily transmitted to the antenna's on- or in-road location, or perhaps due to limits on the amount of power a battery can supply if it is to have a life or re-charge interval that is not too short, etc. Also, in many jurisdictions there are laws or regulations which place restrictions on the amount of power that a radio antenna (including an RFID antenna intended for vehicle detection/identification use) may emit. These things, for example, therefore often place restrictions on the amount of power that may be supplied to the on- or in-road antenna. However, even aside from the above, there are also practical reasons why increasing the power supplied to an RFID antenna, particularly one that is located on or in the road and used for vehicle detection and identification, is undesirable. For example, it was mentioned above that the amount of energy radiated in an “upward” direction from an on- or in-road antenna (i.e. the amount of energy directed vertically upwards perpendicular to the surface of the road) should be limited, largely so as to limit “blinding” reflections from the underside of the vehicles. Simply increasing the amount of power supplied to an on- or in-road RFID antenna used for vehicle detection/identification would not only increase the size of antenna's “read zone” in a radial direction (parallel to the ground), but it would also increase the strength (or power or power density) of the radiation pattern (i.e. increase the amount of radiated power) that is directed in the vertically upward direction (perpendicular to the ground), which would be counter-productive because it would increase the potential for undesirable “blinding” reflections from the undersides of vehicles (among other things). Furthermore, increasing the amount of power that is supplied to an RFID antenna would also likely increase the amount of heat that is generated, not only by the antenna itself, but also (and often much more so) by the associated RFID reader equipment which supplies the power to the antenna (among other things). The amount of heat generated by the antenna and associated RFID reader equipment is extremely important, especially in scenarios where an RFID reader is installed “in-road” because, due to the location and environment in these installations scenarios, there is often very limited possibility for ventilation or other means of heat dissipation. Consequently, minimising the amount of heat that is generated by the antenna and any associated RFID reader (or other) electronics in the first place becomes very important, because the difficulty in ventilating or dissipating heat means that if too much heat is generated in the first place then there may be a danger of overheating the antenna and/or electronics (which may in turn lead to damage or overheating prevention shutdown, if not actual overheating or damage).
Another strategy or design technique used to help in accommodating (or allowing detection and identification of) vehicles travelling at high speeds on freeways or in other open road scenarios—and this is applicable e.g. to the proposals in patent applications '384 and '994—is for the antenna and associated RFID reader equipment to operate with quite a high (or even very high) duty cycle. What operating with a high duty cycle means, in simple terms, is that the RFID reader electronics associated with the antenna cause the antenna to be “powered on”, hence causing the antenna to be radiating radio frequency energy, for a high proportion of the time, or more accurately, for or a high proportion of each signal period. The reason why a high (or very high) duty cycle is often used is, again, to maximise the chance of detecting and reading a vehicle's RFID tag during the potentially short time period while the tag remains in the antenna's read zone. As explained above, this time period is potentially short due to the high speed at which vehicles may be moving in highway scenarios and the consequently limited period of time available to read the tag. However, one of the consequences of using a high duty cycle is that the amount of energy consumed is increased. Basically, the higher the duty cycle, the higher is the energy use and consumption by the RFID reader antenna and it's electronics. Also, it generally follows that the higher the energy use and consumption (in this case due to the use of a high duty cycle) the higher the potential for heat generation.
Designing an RFID reader whose antenna is able to provide a radiation pattern that meets or balances the requirements discussed above, and also where the RFID reader is able to operate with a high duty cycle whilst at the same time ensuring energy use and consumption and heat generation do not exceed acceptable levels, has proven to be extremely challenging. Even so, again, the antenna and RFID reader design(s) described in patent application '994 in particular is presently considered to be promising, and (it is thought) commercially viable, including for “open road” and freeway applications.
However, yet another issue to consider for RFID readers like e.g. the one described in patent application '994, including its antenna and the associated RFID reader equipment (bearing in mind that that RFID reader is considered to be capable of freeway or other open road application), is that, at least for permanent installation scenarios (i.e. where the reader is permanently installed to operate at a single location—as opposed to in a temporary relocatable manner), in order for the RFID antenna to be positioned at the correct position to “read” the tags on passing vehicles (which essentially requires, inter alia, the antenna to be positioned with its base plane parallel and level with the surface of the road), much of the associated RFID reader electronics, casing and also structural components, heatsinks, etc, must be installed “in” the road (i.e. below the road surface). Basically, so that the reader electronics, structural components, etc, in question can remain with or very near by the antenna (as opposed to being located some remote distance away), it is thought that, in permanent installation scenarios, these things really need to be “buried” beneath (or buried very nearby) the antenna in the road, beneath road surface level. One natural consequence of this is that, as part of the installation of such RFID readers, there is a requirement to cut or dig into the road in order to install the RFID reader. This can increase costs associated with the installation. It may often also require temporary closure of the road, or at least of the lane where the RFID reader is being installed. As mentioned above, this can be disruptive and costly. Nevertheless, it is considered that the costs associated with the permanent installation of these kinds of RFID readers remain significantly less than cost associated with construction of over-road gantries and the like, and the costs are therefore thought to remain acceptable, particularly given that such RFID readers are likely to be required only at particular locations when used in freeway and other open road applications. Indeed, the number or density of these kinds of RFID readers required (i.e. required to be permanently installed) in a road system/network deployment is likely to be comparatively low, and the cost of installation is therefore considered likely to be acceptable, particularly in comparison with the far greater cost of over road gantries installations and the like.
RFID readers which are capable of permanent “on-road” installation, and which therefore avoid (at least to some extent) the increased time and cost associated with cutting or digging into the road in order to perform permanent RFID reader installation, have previously been proposed. However, many of these previously proposed designs suffer from other problems or disadvantages, one of which is crosstalk and other RF noise, especially reflected signals from adjacent RFID readers.
Against the foregoing background, it is thought that it would be desirable if an antenna, and preferably also an associated RFID reader structure, could be provided which is capable of permanent or semipermanent on-road installation (not in-road installation—see below) and also suitable (when installed on the road) for reading RFID tags on vehicles' license plates, specifically in applications where vehicles are stationary or travelling at low speeds, such as for example in the above-mentioned kinds of vehicle parking and gating applications.
Even though considerable introductory discussion and background information is provided above, it is to be clearly understood that mere reference in this specification to any previous or existing antenna designs, devices, apparatus, products, systems, methods, practices, publications or indeed to any other information, or to any problems or issues, does not constitute an acknowledgement or admission that any of those things, whether individually or in any combination, formed part of the common general knowledge of those skilled in the field, or that they are admissible prior art.